Method for producing highly oriented product of acrylonitrile polymer

ABSTRACT

A HIGHLY ORIENTED ACRYLONITRILE POLYMER PRODUCT COMPRISING ASSEMBLY OF ORIENTED FIBRILS CAN BE OBTAINED BY PREVIOUSLY MOLDING POLYACRYLONITRILE, ACRYLONITRILE COPOLYMER CONTAINING AT LEAST 75% BY WEIGHT OF ACRYLONTIRILE OR MIXTURE THEREOF INTO A BLOCK PRODUCT AND THEN EXTRUDING THE PRE-MOLDED ACRYLONITRILE POLYMER THROUGH A NOZZLE AT A RATIO EXPRESSED BY REDUCTION OF SECTIONAL AREA OF AT LEAST 3.5 AT A PRESSURE OF 100 TO 50,000 KG./CM.2 AT A TEMPERATURE OF 50* TO 300*C. THUS OBTAINED PRODUCT IS USEFUL AS RAW MATERIALS FOR SYNTHETIC PAPER, NONWOVEN FABRICS, COMPOSITE MATERIALS ETC.

United States Patent 3,803,286 METHOD FOR PRODUCING HIGHLY ORIENTED PRODUCT OF ACRYLONITRILE POLYMER Kazuo Nakatsuka, Tokyo, and Shunsuke Minami and Kenzi Murase, Ontake, Japan, assiguors to Mitsubishi Rayon Co., Ltd., Tokyo, Japan No Drawing. Filed Dec. 16, 1971, Ser. No. 208,874 Claims priority, application Japan, Dec. 16, 1970, 45/112,801 Int. Cl. 132% 1/12; B29c 3/00 US. Cl. 264-331 2 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a highly oriented product of acrylonitrile polymer and a method for producing the product. More particularly the present invention relates to a method for producing a highly oriented acrylonitrile polymer product comprising assembly of highly oriented fibrils by premolding acrylonitrile polymer into a block product and then uniaxially extruding the premolded acrylonitrile polymer, through a nozzle, at a suitable pressure and temperature.

Recently, utilization of fibrils of synthetic high polymers as raw materials for paper, non-woven fabrics and composite materials has become increasingly important. In the field of synthetic paper and nonwoven fabrics, synthetic high polymers are superior to natural high polymers in tear strength, water resistance, chemical resistance, etc., but inferior to natural high polymers in rigidity and toughness.

Furthermore, composite plastic materials have also been widely used for pipes, electric articles, sports-goods, tanks, pressure vessels, etc. and as most of the reinforcing materials therefor, glass fibers, metallic fibers, boron, graphite, etc. have been used. However, because of low aflinity between those reinforcing materials and plastics, various after treatments are required for producing such composite plastic materials and in addition, said reinforcing materials are expensive.

The synthetic fibers obtained by the conventional methods are not suitable as reinforcing materials for plastics. This is attributable to their low Youngs modulus, low rigidity and high elongation. It has been considered that these properties can be improved by forming highly oriented fibrils having a compact structure, but such has not yet been attained by the conventional methods.

During the course of intensive researches in an attempt to easily produce highly oriented fibrils, it has now been found that an acrylonitrile polymer is molded at suitable pressure and temperature to obtain a premolded product and said premolded product is extruded at a predetermined reduction ratio at a suitable pressure and temperature to obtain a highly on'ented product which comprises assembly of highly oriented fibrils and thus obtained product can be easily made into a raw material for paper, nonwoven fabrics and composite materials by the usual crushing methods such as beating, mixer treatment, etc.

The present invention will be more fully explained hereinafter.

The present invention concerns a method for producing a highly oriented product for acrylonitrile polymer which comprises previously molding a polyacrylonitrile, acrylonitrile copolymer containing at least by Weight of acrylonitrile or a mixture thereof into a block product of a predetermined size and then extruding thus obtained premolded block product through a nozzle at a temperature of 50 to 300 C. and under a pressure of to 50,000 kg./cm. in such a manner that the ratio (R) expressed by reduction of sectional area at one step is at least 3.5, preferably 3.5 to 60.0. In the present invention polyacrylonitrile and acrylonitrile copolymer may be pretreated under suitable conditions explained hereinafter. The premolding as mentioned above is effected in order that pressure can be uniformly applied on the polymer at the subsequent extrusion and that the material can be easily handled. As to the premolding condition, it may be carried out at a temperature higher than ambient temperature and at a pressure higher than 100 kg./cm. It is not important whether the premolded product is transparent or not. Therefore, the premolded product may be any product of compression-molding of polymer powders or polymer granules, polymerization-molding of monomer and solvent-casting of polymer. Density of the premolded product is preferably higher than 0.6 g./cm.

The premolded product having a predetermined size is charged into a high pressure extruding cylinder kept at a temperature of 50 to 300 C. and is subjected to extrusion. In this step, since lower coefiicient of friction between the premolded product and the inner surface of the metal cylinder or nozzle makes it possible to more effectively utilize the pressure, suitable lubricating oils such as silicon oil, castor oil, soybean oil, mineral oils, etc. are preferably used. However, the extrusion may be easily carried out without the lubricating oils by suitable combination of the temperature and pressure. The extrusion pressure may vary depending upon kind of polymer and temperature, but productivity is conspicuously reduced at a pressure of lower than 100 kg./cm. and operability of apparatus becomes lower at higher than 50,000 kg./cm.'

The acrylonitrile polymer used in the present invention includes polyacrylonitrile, a copolymer containing at least 75 by Weight of acrylonitrile and a mixture thereof produced by the conventional methods. However, it is preferable for obtaining a highly oriented acrylonitrile polymer product which can be easily fibrillated that said polymer does not display a distinct absorption of tan 6 with an intensity of at least 0.10 at a temperature lower than -20 C. in temperature characteristic of dynamic viscoelasticity measured at C./S. Polymer blends with different kind of polymers may be used under the same extruding conditions with the broader composition ranges. However, when the amount of the other polymers in the polymer blend exceeds 50% in volumeric ratio, those which have a glass transition temperature of lower than 20 C. or of higher than 300 C. are not preferrv Further characteristic of the present invention is that the polymer used has a little limitation in polymerization degree and such polymers as having a low molecular weight at which the usual spinning and extrusion are impossible or having a number average molecular weight of higher than 10,000 may also be used. Furthermore, such acrylonitrile polymers as having been subjected to heat treatment at a high temperature or alkali treatment to give a suitable amount of cyclic structure in a polymer main chain may also be used and in this case, the extruded products, for example fibers or fibrils are markedly excellent in chemical resistance and heat resistance and have a high elastic modulus. That is, above mentioned acrylonitrile polymer in the powdery, granular or premolded form may be subjected to heat treatment at a temperature of 200 to 300 C. in an inert atmosphere or alkali treatment thereby the polymer becomes from yellow to blackish brown color tone. Said polymer 4 beating. Thus obtained fibrils and a shrinkage of 1.5% when heated up to 200 C. and an elastic modulus of 1x10 dyn./cm.

EXAMPLE 3 5 can be used as a starting material in the present mven- Acfylomtl'lle 1 0 containing 9 y welghf tion. vinyl acetate was boiled in 10% solution of potassium It has become clear that thus obtained extruded prodhYd1'0Xide iI1 methanol one 110111 obtfilm p d ucts not only have a high orientation of higher than of Yellowlsh brown- 531d Powders Were deified 70% which is derived from the distribution curve around 10 and then premolded under 3000 atmJcm-z at 100 2g=16 7 in X ray diffraction diagram, but also Show Thus premolded product was extruded through a nozzle a half value width of smaller than 1.0 which is. obtained at a reductlolf ratio of under 2000 kg/cm-z at from the radial distribution curve. For example, the Thus Obtamed strands had brown and Showed half value width of the conventional acrylic fibers in @nsparent appearance- T fibrlls Obtamed' by beatmg X-ray diffraction is at least 1.0 to 3.0, while the ex- Said Strands had an onemaflon of 373% by y truded -fibers according to the present invention have a measurement, a Value of and an elastic half value width of 0.7" to 0.8 and possess compact modulus of 8x101 y structure. Furthermore, it has been surprisingly found that the fibers according to the present invention have lower EXAMPLE 4 shrinkage at a high temperature as compared with the l conventional stretched fibers having the similar orientapolyfcrylomtme W heat treated m [Imogen strezim tion Le. the shrinkage of the former is about one fifih at 280 C. for 15 minutes to obtain powders of blackish or onefiflieth of that of the latter brown. The powders were premolded under 3000 kg./ The extruded product according to the present invent' s Thus g z i fp g g tion comprises assembly of fibrils having the characterg 3 i i g h istics as mentioned above, and has an apparent density i er a o 0 am 8 5 avwhich is more than 0 7 times that of the starting poly rug black color and transparent appearance. Said strands met and has such ansparency that it Seems to be showed substantially no thermal shrinkage when heated s o hardly fibrillated by beating operation, etc. The product up to 200 i z iag 3 g X- is ideal extruded material which can be easily handled my .measuremen a a 3 ue W1 2 an an and storaged' elastic -modulus of 1.1 X 10 dyn./'cm. The strands could The ultilization of the fibrils from the products accordfi gi ggggg i beatmg' ing to the present invention gives unexpected characteristics to synthetic paper, raw material of composite maf -f ghlghl-y oriented product terials, nonwoven fabrics, etc. The extruded product o acry ommepo ymer W .compnses itself may be used as it is, in accordance with the uses. (a) premoldmg icrylommle pollyr-ner selected from The present invention will be illustrated in the followthe: i conslstmg of aCWIPIiImIB homopolymer ing examples acrylomtnle copolymer containing at least 75% by EXAMPLE 1 weight of acrylonitrile and less than 25% of at least 40 one monoethylenically unsaturated monomer co- Acrylomtrile polymer powders having a numerical polymerizable with acrylonitrile and mixtures thereaverage molecular we ght of 100,000 shown in Table 1 of, into a block product at a temperature higher than were prepared by precipitauon polymerization with redox ambient temperature and at a pressure higher than catalyst of ammomum persulfate and sodium bisulfite. 100 kgjcm. the resulting premolded acrylonitrile The polymer powders thus prepared were premolded and polymer having an apparent specific gravity of then extruded through a nozzle under the conditions higher than 0.60 g./cm. shown m Table 1. (b) extruding the thus premolded acrylonitrile polymer TABLE 1 Pro-molding Extruding m conditions conditions Apparent Temp Pressure Temp Pressure gi ii Fibriliifi v h ei $533; Polymers 0.) (kg/cm!) C.)- (kg/emf) ratio lation percent; width (gJcmJ) 100 450 130 7, 000 o. 7 0 s4. 0 0. 1. 16 160 450 180 ,3,000 as o 87.0 0. 78 1.18 130 50 15, 000 12. 0 0 92. 0 0. .3 1. is 130 450 130 4, 000 s. s o as. 1 0. s0 1. m

50 450 7,000 0., o 85.0 0.84 1.15 100 450 5,000 4.5 o 80.0 0. 79 1.00 450 100 30, 000 o. 5 0 s4. 0 0. 79 1. 15 Fibers according to the conventional stretching (PAN) X 88. 0 l. 11 1. 19

I Stretching to 12 times.

EXAMPLE 2 through a nozzle at a ratio expressed by reduction 1 area of at least 3.5 under a ressure of Polyacrylonitrile having a polymerization degree of of Sectlona p a 100,000 which was heat treated in nitrogen stream at ggf at a temperature of 50 to 6 p 2: 3' 2: g g s :3: fi$zi g gg 70 2. A method according to claim 1, wherein the starting truzicd through'a nozzle 21': a reducticn ratio of 115 acrylonitrile polymer is subjected to heat treatment in under 5000 kgJcm. at 130 C. Thus obtained extruded the powdery granular preniolded form at a temper?- product had blackish brown color at normal tempera ture of 200 to 300 C. in an inert atmosphere to obtam ture, an orientation of 89.8% by X-ray measurement and 75 yellow b'mcklsh brown P a half value width of 0.73 and could be fibrillated by (References on following page) 5 6 References Cited 3,493,648 2/1970 Griflith 264-176 R 3,531,452 9/1970 Griflith et a1 264-235 UNITED STATES PATENTS 3,662,052 5/1972 Nowak et a1 264-294 2,585, 2/1952 Cox 264 3,714,320 1/1973 Shaw 264- 176 R 2,710,846 6/1955 Dietrich etal 264-182 5 2,953,816 9/1960 Kidder 264-323 JAY H. WOO, Primary Examiner 2,987,775 6/1961 Albrccht et a1. 264-323 3,412,177 11/1968 Grifiith 264 331 US. Cl. X.R. 3,437,726 4/1969 Hagmann 264323 264176 R, 329

3,470,291 9/1969 Johnson 264292 10 

